The U.S. Centers for Disease Control and Prevention say the director of the laboratory that released anthrax by mistake last month has left the agency.

The CDC said Michael Farrell, the head of its Bioterror Rapid Response and Advanced Technology Laboratory, resigned Tuesday, after a mix-up in June potentially exposed dozens of people to the deadly bacteria.

Potentially 80 government lab workers were exposed to anthrax when samples of the bacteria were released before they were deactivated.

None of the lab workers has shown any sign of illness.

Farrell led the CDC’s bioterror lab in Atlanta starting in 2009. He was reassigned after the anthrax scare.

An investigation into the incident revealed lax safety and security standards.